Reduced folate carrier polymorphism determines methotrexate uptake by B cells and CD4+T cells

Objective. To examine if polymorphism 80G -> A in the Reduced Folate Carrier (RFC) affects uptake of MTX in B- and CD4+ T-cells. Methods. Mononuclear cells were isolated from peripheral blood of healthy persons. Real-time PCR was used to detect the RFC80 variants. FITC-labelled MTX was added to cells stimulated with Candida albicans or tetanus toxoid, and the uptake of MTX was measured by flow cytometry. A FITC-conjugated monoclonal antibody against RFC was used to detect the cellular RFC expression. Results. Anti gen-stimulated CD4+ T cells and B cells from individuals with the GG variant (n=9) exhibited lower uptake of MTX than individuals expressing the AA variant (n=8), or the GA variant (n=8). No difference could be demonstrated between the three groups with respect to the expression of RFC by CD4+ T cells and B cells, and CD4+ T cells from individuals homozygous for the G allele exhibited lower uptake of MTX per receptor than CD4+ T cells from individuals homozygous for the A allele. Conclusion. MTX is taken up more efficiently via the A allele than via the G allele. This difference between the variant forms of RFC suggests that genotyping could be relevant for determining the relevant dosage of MTX in the treatment of neoplastic and autoimmune disease.